The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Friction clutch packs, that is, clutches and brakes having first and second interleaved pluralities of clutch plates compressed axially by an actuator to effect torque transfer are extraordinarily common components in modern automatic motor vehicle transmissions utilizing a plurality of planetary gear assemblies. Numerous features such as compact size, high torque transfer capability, modulating or proportioning capability and flexibility of configuration account for this popularity.
Such friction clutch packs, especially friction brakes wherein one of the pluralities of clutch plates is stationary, are not without certain disadvantages. One of the most significant disadvantage results from the basic construction of the clutch: the pluralities of interleaved clutch plates. When a first plurality is stationary or rotating at a relatively slow speed and the second plurality is rotating at a relatively high speed, the resulting frictional losses, referred to as spin losses, caused by multiple surfaces rotating against one another with only negligible axial spacing between them, can be significant, and especially so at higher speeds.
Another disadvantage related to both the small inter plate spacing and high rotational speeds of friction clutches or brakes is plate flutter. The first mode of structural vibration of a disc or plate is bending about one of the discs axes. Flat discs or plates provide no means to impede this first mode of vibration. Clutch plate flutter is the tendency of clutch plates to develop standing waves as they rotate, again particularly at high rotational speeds which may readily be in the range of from 8,000 to 12,000 r.p.m. The standing waves may distort the edge of the clutch plate so that it has a sinusoidal periphery and the wave may travel with or against the direction of rotation of the clutch plate.
It has been determined that such standing waves, which may develop in one or several clutch plates, exacerbate the spin loss problem. This occurs because the crowns or raised regions of the distorted plates are concentrated areas of frictional contact with adjacent plates and these concentrated areas of heat generation form hot spots on the surfaces of the plates which can cause thermal degradation of the friction material.
From the foregoing, it is apparent that reducing or eliminating the generation of bending and plate flutter in the plates of friction pack clutches and brakes rotating at high speeds would be beneficial and the present invention is so directed.